The subject matter disclosed herein relates generally to imaging systems, and more particularly to a radio frequency (RF) body coil for dual-modality imaging.
Magnetic resonance imaging (MRI) is a medical imaging modality that generates images of the inside of a human body without using x-rays or other ionizing radiation. MRI uses a magnet to create a strong, uniform, static magnetic field (i.e., the “main magnetic field”) and gradient coils to produce smaller amplitude, spatially varying magnetic fields when a current is applied to the gradient coils. When a human body, or part of a human body, is placed in the main magnetic field, the nuclear spins that are associated with hydrogen nuclei in tissue water become polarized. The magnetic moments that are associated with these spins become preferentially aligned along the direction of the main magnetic field, resulting in a small net tissue magnetization along that axis (the “z axis,” by convention) and the gradient coils encode the MR signal.
RF coils are used to create pulses of RF energy at or near the resonance frequency of the hydrogen nuclei, also referred to herein as the Larmor frequency. These RF coils are used to transmit RF excitation signals and receive MR signals used to form the images. Various types of RF coils may be used in an MRI system such as a whole-body RF coil and an RF surface (or local) coil.
It may be desirable to incorporate the functionality of a positron emission tomography (PET) imaging system and the functionality of the MRI imaging system in a dual-modality imaging system. To form the dual-modality imaging system, the RF coil and a PET detector are both arranged within the magnet. For optimal imaging system performance, it is desirable that the PET detector and the RF coil occupy the same general physical space within the magnet. Moreover, conventional PET detectors are relatively heavy and should be supported and held in place with positional accuracy. Additionally, the PET detectors should be shielded from the RF generated by the RF coil. However, the addition of the PET detectors within the MRI imaging system may reduce the size of the patient bore and therefore limit the size of a patient that may be scanned using the dual-modality imaging system.